218 REPORT—1896. 
3. Experiments inside the hut, within 3 feet S. side and 7 feet 
N. side of the instrument. 
Effect of 240 lb. Zero 59. 
On North side, Reading 60°5. Effect 15=0'-49 
» South ,, - 54:5. > 4:5=1':48 
» North. ,, o 60°5. 
Effect of 570 lb. Zero 59. 
On South side, Reading 50. Effect 9=2'":97 
» North ,, 3 66. (=203 
4. Experiment with load outside the hut within 5 feet on 8S. side 
and 5 feet on N. side. 
Effect of 570 lb. Zero 56. 
On South side, Reading 5 
» North ,, ee 5 
»  15=0":49 
” 
5. Effect 1=0''-33 
5. Oe 0 
This last reading is unsatisfactory. Five minutes later it became 55:5, 
but if the north side load showed an effect it ought to have exceeded 56. 
In the afternoon a few experiments were made in the main building of 
the Observatory. The horizontal pendulum was placed on the top of a 
massive pier whilst two boys and a man (almost 350 Ib.) stationed them- 
selves in the basement of the building, first on the east side and then on 
the west side of the same. The difference in readings given by the two 
positions was approximately 0-16. 
V. The Perry Tromometer. By Professor Joun Perry, F.#.S. 
What is interesting about the apparatus is this, that any periodic 
motion of the supports is faithfully indicated by the pointer if its frequency 
is several times the natural frequency of vibration when its supports are 
at rest. 
One body supported on a pivot with three Ayrton-Perry springs will 
record the vertical and two horizontal motions. 
A body P G Q is free to move about an axis P at right angles to the 
paper. G is its centre of gravity. An Ayrton-Perry spring is applied 
HiGwete: 
vertically at Q from the point A. Weight of body is W. Vertical force 
at P is P, force at Qis Q. Let P and A get a vertical displacement ~, 
downward, and let Q be displaced « downward. Let Q=Q,+¢(a—2,) 
where c represents the constant of the spring. Then forming the equations 
of motion we find, neglecting friction 
etn esen,+nrx, . ” ‘ (1) 
